1. Field of the Invention
This invention relates to interference fit joints and more particularly to tools containing such joints.
2. Description of the Prior Art
Interference fit joints on many tools, such as indexable ratchet wrenches, were previously formed by internal splines defining an aperture on an outer member, such as a ratchet head, and external splines on an inner member, such as an indexable pin. The internal and external splines were usually similarly shaped and each included a crest and side flats and was separated from adjacent splines on the member by valleys. Typically, when the first and second members were pressed together, they contacted each other at the crests, side flats, and valleys. Though this structure provided a good connection, the interference between the crests and valleys created hoop stress on the outer member and many times would cause cracking of the outer member. The tolerances of the external and internal splines would therefore need to be closely controlled during manufacture to aid in preventing cracking.
Some interference fit joints have been formed which do not have as much of a hoop stress problem. These joints are, however, either non-permanent, costly or subject to other problems.
For example, one such interference fit joint previously formed includes identically shaped internal and external splines engaging each other only on respective side flats. The splines are slid together and then the external splines are urged outward toward the internal splines by a threaded member to produce the interference fit between the flats of the splines. The structure forming the fit, however, is costly and does not form a permanent joint.
Another prior interference fit joint having reduced radial hoop stress includes internal splines and external splines where only one of the side flats of either the external splines or the internal splines has a slight helical angle which forms an interference fit with a facing flat of an engaged spline. This structure, however, cantilevers the splines and could cause fracture of the splines at the valleys between the splines.